David R. Bridgland

River terrace systems in north-west Europe: an archive of environmental change, uplift and early human occupation

Abstract Staircases of large-scale aggradational river terraces are a notable feature of many valleys in the temperate lattitudes, particularly in areas beyond the reach of the erosive activities of Pleistocene ice sheets. It is now recognized that the cyclic fluctuations of climate during the Quaternary have driven the generation of terraces, through the direct and indirect influence of both temperature and precipitation on fluviatile activity. Where fossiliferous deposits are preserved within terrace sequences it is often possible to date these and to correlate them with the oceanic record, thus providing an important framework for the evidence of environmental change on land. Middle and Late Pleistocene terraces in different areas can commonly be seen to have formed in synchrony with glacial–interglacial cycles or with longer-periodicity megacycles. Climatic forcing alone is insufficient to cause terraces to form, however; uplift is also necessary, so that terrace sequences can provide a useful record of crustal movement. In northwest Europe, where some of the best known studies of river terrace sequences have been carried out, the fluviatile deposits are also an important repository for Palaeolithic artefacts, from which a record of early human occupation can be reconstructed.

Quaternary of the Thames

The Pleistocene of the Thames the upper Thames basin the middle Thames the lower Thames Essex.

Uplift-driven valley incision and climate-controlled river terrace development in the Thames Valley, UK

Abstract The sequence of terraces of the River Thames in southeast England has previously been shown to span the period from the earliest Pleistocene to the present. This terrace sequence contains biostratigraphical and sedimentary evidence that testifies to the high-amplitude climatic changes of the Quaternary. Large-scale fluvial incision, resulting in basin-wide terrace formation, appears to have been concentrated at the warming limbs of the major climatic glacial–interglacial cycles, when sediment supply was greatly reduced. This incision and subsequent valley-floor widening created the accommodation space for the later aggradation of the terrace sediments during the following warm–cold transitions and during the cold stages, when high-sediment supply conditions prevailed. Although the timing of terrace aggradation may be controlled by climate change, the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of Quaternary climatic change alone and recently developed models suggest that long-term incision by the Thames has been driven by uplift. This paper presents an overview of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons. Superimposed upon these broad changes, revealed by the complex internal sedimentary architecture of many terrace sediments, are the geomorphological system responses to both higher-frequency climate-driven changes and more localized intrinsic fluvial system adjustments.

Crustal uplift in southern England: evidence from the river terrace records

Abstract Much of the past work on the Quaternary rivers of northwest Europe has been concerned with river terraces, which characterise almost every valley. While these terraces are undoubtedly striking features of the landscape, the incision achieved by Quaternary rivers is equally significant in terms of river behaviour, and for an understanding of the factors affecting landform development during the Quaternary. This paper examines the incision achieved during the Quaternary by the Thames, in both its upper and lower catchments, and by the Hampshire Avon in southern England. Valley incision rates of ca. 0.07–0.10 m ka −1 have been identified, although in the lower catchment of the Thames, these have been enhanced by additional incision in response to glacio-isostasy and valley shortening. A model is proposed in which regional uplift is recognized as the primary cause of incision by these Quaternary rivers. Possible mechanisms for regional uplift are considered.

Sedimentology, palaeontology and archaeology of late Middle Pleistocene River Thames terrace deposits at Purfleet, Essex, UK

Middle Pleistocene fluvial deposits of the Corbets Tey Formation at Purfleet, Essex, provide evidence of an un-named and previously poorly recognized interglacial, thought to corrrelate with Oxygen Isotope Stage (OIS) 9. Previous attributions of the sediments to the Ipswichian (Last Interglacial) Stage are refuted. New investigations have yielded rich molluscan, mammalian and ostracod assemblages that indicate fully temperate conditions and the distal influence of marine transgression. Pollen analyses suggest a previously unrecorded phase of interglacial vegetational development. Clast composition, geomorphological evidence and the occurrence of molluscs that favour large rivers all point to deposition by the Thames, rather than in a minor tributary, as suggested previously. Three separate Palaeolithic industries in stratigraphical superposition are recognized at Purfleet, these being Clactonian, Acheulean and Levallois. Purfleet is therefore a key locality in the understanding of the early human occupation and exploitation of southern Britain, as well as for the interpretation and correlation of the terrace sequence in the Thames Valley.

A chronological framework for the British Quaternary based on Bithynia opercula

Marine and ice-core records show that the Earth has experienced a succession of glacials and interglacials during the Quaternary (last ∼2.6 million years), although it is often difficult to correlate fragmentary terrestrial records with specific cycles. Aminostratigraphy is a method potentially able to link terrestrial sequences to the marine isotope stages (MIS) of the deep-sea record. We have used new methods of extraction and analysis of amino acids, preserved within the calcitic opercula of the freshwater gastropod Bithynia, to provide the most comprehensive data set for the British Pleistocene based on a single dating technique. A total of 470 opercula from 74 sites spanning the entire Quaternary are ranked in order of relative age based on the extent of protein degradation, using aspartic acid/asparagine (Asx), glutamic acid/glutamine (Glx), serine (Ser), alanine (Ala) and valine (Val). This new aminostratigraphy is consistent with the stratigraphical relationships of stratotypes, sites with independent geochronology, biostratigraphy and terrace stratigraphy. The method corroborates the existence of four interglacial stages between the Anglian (MIS 12) and the Holocene in the terrestrial succession. It establishes human occupation of Britain in most interglacial stages after MIS 15, but supports the notion of human absence during the Last Interglacial (MIS 5e). Suspicions that the treeless ‘optimum of the Upton Warren interstadial’ at Isleworth pre-dates MIS 3 are confirmed. This new aminostratigraphy provides a robust framework against which climatic, biostratigraphical and archaeological models can be tested.

The Middle and Upper Pleistocene sequence in the Lower Thames: a record of Milankovitch climatic fluctuation and early human occupation of southern Britain: Henry Stopes Memorial Lecture 2004

The sequence of Pleistocene river terraces in the Lower Thames, long recognized as an important repository of evidence for Palaeolithic human activity, can now be interpreted in the context of the last five Milankovitch (100 ka) climate cycles, beginning with cold marine oxygen isotope stage (MIS) 12, when ice sheets blocked an earlier Thames course in Hertfordshire and Essex. This interpretation stems from empirical evidence from the Lower Thames deposits, in which the preservation of faunal and archaeological remains is unusually common. These deposits were laid down as climatically generated river terraces, formed in synchrony with the climatic cycles, although the progressive incision to ever-lower valley-floor levels is a response to background uplift. Interpretation of this evidence is revised here for the Dartford-Purfleet area in recognition of a phase of minor downcutting at the ends of interglacials. Previously regarded as insignificant, it is now realized that this erosion phase has resulted in interglacial sediments forming the higher of two facets within each terrace in the Lower Thames. Guided by this revision, the Lower Thames (Thames-Medway) terrace sequence further downstream, in eastern Essex, is reappraised in the light of the better preserved and better understood record from the Dartford-Purfleet area. It is concluded that Thames-Medway drainage northwards to the Clacton area (NE Essex) persisted until after the Hoxnian (MIS 11), so that the Clactonian (Palaeolithic) type locality lay in the main Thames valley at the time when the Clactonian knappers were operating. Despite its relegation in recent years from the earliest British Palaeolithic culture to little more than a curious anomaly, with doubts expressed about its separate existence, recent interpretations of the Clactonian hold that it appeared within the Thames sequence on two separate occasions, both coincident with a glacial to interglacial transition. These separate Clactonian occupations, at the MIS 12-11 and 10-9 transitions, together with the first appearance of the Levallois technique at around the MIS 9-8 boundary, can be linked to the chronology and to the cyclic climatic record that together underpin the Lower Thames sequence.

The Pleistocene fluvial stratigraphy and palaeogeography of Essex

Four main types of fluvial gravel aggradation are recognised in Essex, distinguished regionally, lithologically and by stratigraphic and altitudinal position. Firstly, deposits which are widespread in the northern and central parts of the county form part of the Kesgrave Sands and Gravels, which represent terrace aggradations of the pre-diversion Thames. A second type comprises the terrace gravels of the Lower Thames, which continue the history of the river after its glacial diversion into its modern valley through London. The third type, the High-level East Essex Gravel, comprises the degraded remnants of Medway deposits laid down by that river in eastern Essex at broadly the same time as the deposition by the Thames of the Kesgrave Sands and Gravels. Finally, a number of further aggradations, grouped together under the title Low-level East Essex Gravel, complete the terrace sequence in eastern Essex. These last deposits are of Thames-Medway origin, therefore representing a downstream continuation of the Lower Thames terraces. The change from Medway to Thames-Medway gravels in eastern Essex indicates that the glacially diverted Thames adopted the pre-existing valley of the Medway. This post-diversion route of the Thames-Medway was progressively modified in successive terrace aggradations, culminating in the pre-Flandrian buried valley which underlies the modern Thames estuary. The reconstruction of palaeodrainage and terrace stratigraphy in Essex promises to provide important links between the Quaternary sequences of the Thames basin and East Anglia.

A revised model for the Pleistocene development of the River Avon, Warwickshire

A re-examination of the Pleistocene river deposits in the valley of the Midland Avon indicates that the conventional post-Hoxnian model for their development has to be revised. Reinvestigation of two key localities, Cropthorne in the Lower Avon valley and Ailstone on the Warwickshire Stour, a left bank tributary of the Avon, shows that the deposits of at least two separate temperate episodes are represented within the sequence. Amino-acid ratios on non-marine Mollusca from the temperate deposits allow these episodes to be correlated with oxygen isotope stages 5 and 7. Since the stage 7 temperate deposit lies within sediments which post-date the Wolston glacial sequence. an older age is indicated for that sequence than is proposed in the conventional stratigraphic succession of the British Pleistocene.

Correlation of English and German Middle Pleistocene fluvial sequences based on mammalian biostratigraphy

In this paper interglacial mammalian assemblages from key Middle Pleistocene fluvial sites in Germany are compared to Mammal Assemblage-Zones (MAZs) recently established in the post-Anglian/Elsterian sequence of the Lower Thames, U.K. It is believed that four separate interglacials are represented by the Lower Thames MAZs, correlated with oxygen isotope stages (OIS) 11, 9, 7 and substage 5e (although the last of these is Late Pleistocene). Nowhere in Germany can a full sequence of these interglacials be identified from mammalian evidence in a single terrace staircase, as is the case in the Lower Thames, although further research on the Wipper terraces at Bilzingsleben may identify such a sequence. It is also possible that the sequence of overlapping fluvial channels in the lignite mine at Schoningen will eventually produce a comparable mammalian story. Excellent correspondence has been recognized between the mammalian assemblages at Steinheim an der Murr and Bilzingsleben II and the Swanscombe MAZ from the Thames. These three sites are attributed to the Hoxnian/Holsteinian interglacial and are thought to correlate with OIS 11. Close comparison can also be made between the mammalian sequence from the celebrated travertine locality at Weimar-Ehringsdorf and two separate MAZs from Aveley, in the Thames, attributed to separate substages of OIS 7. An equivalent to the Purfleet MAZ of the Thames, which is believed to correlate with OIS 9, has yet to be identified in Germany.